The capacity of lymphocytes to recognize and distinguish foreign antigens from self antigens and mount an immune response is a consequence of the cell surface receptors. The T cell receptor plays a pivotal role in this decision making yet the molecular basis for this recognition is not precisely understood. The recognition of various forms of processed antigen by either cytotoxic T cells or helper T cells is one of the most important interactions that occurs in the immune system. The current lack of structural information is in part a consequence of the lack of these heterodimeric molecules in soluble form. This proposal seeks to answer some of these basic questions using an expression system that has been developed to produce soluble recombinant heterodimeric T cell receptors using a T cell thymoma. Initial characterization of two different recombinant receptors suggests they are indistinguishable from normal receptors produced on T cell clones by all available anti- clonotypic monoclonal antibodies and properties on polyacrylamide gels. A primary goal of this proposal is to extend the biochemical characterization of these TcRS, produce significant amounts of pure receptors and to develop methods for analysis of TcR interaction with MHC molecules. Both alloreactive MHC class I restricted and antigen specific MHC class II restricted TcRs will be analyzed for specific binding to the specific antigen plus MHC molecules. Several approaches will be used to determine whether it is possible to measure an affinity for this interaction. The properties of a receptor specific for the Ld class I antigen and a conalbumin specific class II restricted receptor will be studied. A source for appropriate recombinant MHC class I antigen exists. Production of the appropriate MHC class II molecules required for analysis of the D10 TcR will be developed utilizing existing technology. Finally, a strategy for generating single chain TcRs will be developed for these TcRs using strategies that have been successful with immunoglobulins and one TcR. The functional and binding assays for this new potential source of recombinant TcRs are available.